1. Field of the Invention
The present invention relates to polymer blend fibers having a phase separation structure and a method for producing the same. More specifically, the present invention relates to polymer blend fibers capable of providing various characteristics (e.g., light-weight, water and moisture absorption, dyeability, thermal insulation, touch, water and oil repellency, and heat resistance) depending upon the use, due to a variety of precisely controlled phase separation structures.
2. Description of the Related Art
Mixed-spinning using polymer blends has been tried for the purpose of improving the characteristics of synthetic fibers. Mixed-spinning has various objectives. It is considered that synthetic fibers with their various characteristics improved can be obtained by appropriately selecting the kind of polymers constituting a polymer blend and the blend ratio thereof. Therefore, mixed-spinning has been utilized in order to improve the characteristics of synthetic fibers, such as dyeability, moisture absorption, specific gravity, a cross-linking effect, a viscoelastic property, feeling, and touch.
In the case where mixed-spinning is conducted so as to improve the characteristics of synthetic fibers, a melt spinning method is typically utilized, which uses a polymer blend composed of polymers which are incompatible with each other. This is because synthetic fibers are considered to be provided with various characteristics depending upon the use by utilizing the nonuniformity (i.e., a continuous phase and a disperse phase) of a phase separation structure formed from such a polymer blend. For example, the following use of a continuous phase and a disperse phase of a phase separation structure has been expected: (1) by allowing a component forming a disperse phase to react with an appropriate pharmaceutical agent, the disperse phase is provided with water or oil repellency. As a result, fibers with better water or oil repellency compared to those obtained by surface processing can be obtained. (2) An appropriate chemical treatment is conducted to extract a disperse phase, thereby forming hollow portions in fibers. As a result, (2-a) these hollow portions make the fibers light-weight; (2-b) the fibers are provided with a warmth retaining property because of the thermal insulating effect of the hollow portions; (2-c) the hollow portions can absorb water so that the fibers have water and moisture absorption; specifically, fibers with dry touch can be obtained; and (2-d) fibers are provided with dyeability by allowing the hollow portions to accomodate a dye.
However, in the case where melt spinning is conducted by using a polymer blend composed of polymers which are incompatible with each other, it is substantially difficult to obtain a stable polymer blend melt. For this reason, the melts of polymers constituting the polymer blend are extruded from different nozzles and polymer melts are physically mixed at the time of extrusion, whereby melt spinning is conducted. According to such physical mixing, fibers having a precisely controlled phase separation structure cannot be obtained easily. Thus, it is substantially impossible to obtain various phase separation structures depending upon the use by this method.
In order to solve the above-mentioned problems, Japanese Laid-Open Patent Publication No. 4-209824 discloses a method of preparing a polymer blend melt composed of polymers which are incompatible with each other by using a compatibilizer, thereby conducting melt spinning. Japanese Laid-Open Patent Publication No. 6-2267 discloses composite fibers obtained by extruding polymer blends each forming a sea-island structure and each having a particular difference in fusion viscosity so as to attach to each other.
However, these attempts do not control the phase separation itself, and as a result, the substantial problems of polymer blends composed of polymers which are incompatible with each other cannot be solved. More specifically, in melt spinning using such polymer blends, the following problems remain unsolved: (a) fibers cannot be provided with desired characteristics depending upon the use because of difficulties with phase separation control; (b) high-speed spinning is difficult to conduct due to unsatisfactory spinnability, resulting in poor productivity; (c) since the size and the variation in size of a disperse phase are large, mechanical characteristics of fibers to be obtained are insufficient; and (d) compatibilizers or the like is required to be used, so that costs increase.
As described above, polymer blend fibers having a precisely controlled phase separation structure and a method for easily producing such fibers are desired.